Using spontaneously hypertensive rats (SHRs), attempts were made to decide whether or not mechanical stress on the femoral head plays a role in the occurrence of the femoral bead lesions, namely, avascular necrosis and ossification disturbance. The following measures were taken to reduce mechanical stress : severing of the sciatic nerve, severing of both the sciatic and femoral nerves, and amputation of the hind limb on one side. The frequency of the femoral head lesions was highest in the control group (85%). It was lower in the sciatic nerve severance group, sciatic and femoral nerve severance group, and hind limb amputation group, in that order, showing a direct correlation with the level of mechanical stress. Moreover, histological abnormalities of the growth plate were observed frequently in the outer portion of the femoral head in SHRs with femoral head lesions.These findings indicate that-mechanical stress causes an impairment of the femoral head cartilage, resulting in the obst
… Moreruction of blood vessels leading to the epiphyseal nucleus of the femoral head.The growth plate of the femoral head in growing SHRs was investigated histologically and ultrastructurally. As compared with the normal femoral heads, histological abnormalities of the growth plate in the weight-bearing area of the femoral heads, such as decreased thickness and nodular formation etc., frequently accompanied femoral head lesion. Ultrastructural observation disclosed that the most of chondrocytes in the growth plate with, decreased thickness were in the degenerative condition. Chondrocytes in nodular formation showed the fine structure reflecting the accelerated cell metabolism or mild degeneration indicating the regenerative process.It suggested that the disorder o f chondrocytes would weaken the architecture of the cartilaginous canal where the blood vessels pass of the proximal femoral epiphysis, and that the obstruction of the cartilaginous canal would cause. the femoral head lesions in SHRs.The articular and growth cartilage in the femoral head was observed histochemically in 50 SHRs at the age of 5-9 weeks after birth.In the period of 5-7 weeks after birth, abnormal findings of the cartilage appeared in the outer part of the femoral head where toluidine. blue stain disclosed-the decreased stainability. So, it suggests that abnormalities of the cartilage in the femoral head may take part in the occurrence of osteonecrosis of the femoral head in SHRs. Less